Pneumatically-actuated on/off or control valves which open and close non-electrically are known in the art. Such valves may include, for example, a piloted actuator which is opened and closed by a pneumatic control fluid source which is connected to an input port on the valve. Movement of the piloted actuator is caused by a pressure differential created across the actuator by the control fluid.
Movement of the actuator may be used to perform a wide variety of functions. For example, movement of the actuator may control the flow of a second fluid source which is connected to a second input port on the valve. This type of valve acts as a "sentry" by "sensing" the input of the control fluid, and then acts as a "trigger" to actuate and/or control the flow of the second fluid through the valve.
Known pneumatically-actuated valves typically include multiple seals, springs, bellows, diaphragms and other internal components which create internal resistance to movement of the actuator. In order to operate properly, such known pneumatically-actuated valves require the input of a high-pressure control fluid which creates a force sufficient to overcome such internal resistance. Further, such internal resistance in prior art valves may spark an explosion if used in an environment containing nitrous oxide, oxygen or other flammable gases. It would be desirable to provide a pneumatically-actuated valve whose design has reduced internal resistance to movement of the actuator.
Many applications require a pneumatically-actuated valve which is responsive to the input of a low-pressure control fluid or a low-flow-rate control fluid. As used herein, "low pressure" is used to refer to pressure slightly above atmospheric pressure and "low flow rate" is used to refer to flow rates of about 1/2 liter/minute or less. For example, gaseous anesthesia/analgesia provided to a dental patient is typically supplied at a pressure of less than 1 p.s.i. and a flow rate of about 3-10 liters per minute. Prior art pneumatically-actuated valves are typically designated to operate effectively only when connected to a high-pressure control fluid such as 100 p.s.i. It would be desirable to provide a pneumatically-actuated valve which is actuated by the input of a low-pressure or low-flow-rate control fluid such as gaseous anesthesia/analgesia.
As described above, prior art pneumatically-actuated valves have been used to trigger and/or control the flow of a second fluid through the valve. In the dental field, the second fluid typically comprises a mixture of gases exhaled by a patient into an anesthesia/analgesia scavenging mask. The mixture of gases is suctioned from the mask by a vacuum source which is connected to and controlled by an on/off valve. The on/off valve is very hard to initially break free from the closed position because the vacuum source exerts a high suction force on the actuator when the actuator is at or near the closed limit position. To overcome the high suction force, prior art pneumatically-actuated valves require the input of a high pressure control fluid to operate effectively when connected to a high-pressure vacuum fluid source. Therefore, it would also be desirable to provide a pneumatically-actuated valve which can be actuated by a low-pressure control fluid source and when connected to a second high vacuum pressure fluid source.
In many applications, especially dental anesthesia/analgesia applications, the flow rate of control fluid and the flow rate of the second fluid should be proportionally controlled. For example, the flow rate of anesthesia/analgesia delivered to the patient should be proportional to the flow rate of exhalation gases removed by the vacuum source. Prior art pneumatically-actuated valves typically do not automatically regulate the flow rate of the second fluid in proportion to the flow rate of the control fluid. It would also be desirable to provide a pneumatically-actuated valve which is self-regulating so that the flow rate of the second fluid is automatically controlled in proportion to the flow rate of the control fluid.
In dental anesthesia/analgesia applications, it is critical that the vacuum source be activated at or around the same time a supply of anesthesia/analgesia is delivered to the patient. If excess anesthesia/analgesia and exhalation gases from the patient are not scavenged by the vacuum source, a potentially hazardous condition builds up in the treatment room. In prior art anesthesia/analgesia configurations, the vacuum source is activated by a manual control valve which must be opened by an operator independently from the valve controlling the flow of anesthesia/analgesia/analgesia. Not surprisingly, cases have been reported wherein the vacuum-source control valve was not opened during the operation due to human error. Therefore, it would also be particularly desirable to provide a control valve for an anesthesia/analgesia delivery system which automatically activates the anesthesia/analgesia scavenger or vacuum source at the same time anesthesia/analgesia is delivered to a patient.